Heart disease, specifically coronary artery disease, is a major cause of death, disability, and healthcare expense. Coronary artery disease (CAD) results from arteriosclerosis of blood vessels serving the heart. Arteriosclerosis is a hardening and narrowing of the arteries commonly accompanied by a deposition of a waxy substance. This substance, known as plaque, is made of cholesterol, fatty compounds, calcium, and the blood-clotting material fibrin. Often the arteries of the heart can suddenly become so severely blocked that there is an inadequate blood supply after the blockage, leading to the occurrence of a myocardial infarction or “heart attack.” Although some heart attacks are caused by such “hard” plaques, many are caused by “soft” or vulnerable plaques. A vulnerable plaque is an inflamed part of an artery that can burst. This can lead to the formation of a blood clot, which can reduce or block the flow of blood.
Plain-old-balloon-angioplasty (POBA) is an exemplary medical procedure to widen obstructed blood vessels narrowed by plaque deposits. The procedure may be used in coronary or peripheral arteries. In an angioplasty procedure, a catheter having a special inflatable balloon on its distal end is navigated through the patient's arteries and is advanced through the artery to be treated to position the balloon within the narrowed region (stenosis). The region of the stenosis is expanded by inflating the balloon under pressure to forcibly widen the artery. After the artery has been widened, the balloon is deflated and the catheter is removed from the patient.
A significant difficulty associated with balloon angioplasty is that in a considerable number of cases the artery may again become obstructed in the same region where the balloon angioplasty had been performed. The repeat obstruction may be an immediate abrupt closure, which is usually caused by an intimal flap or a segment of plaque or plaque-laden tissue that loosens or breaks free as a result of the damage done to the arterial wall during the balloon angioplasty. More commonly, closure of the artery (restenosis) may occur at a later time, for example two or more months after the angioplasty, for reasons not fully understood and may require repeat balloon angioplasty or bypass surgery. When such longer-term restenosis occurs, it usually is more similar to the original stenosis, that is, it is in the form of cell proliferation and renewed plaque deposition in and on the arterial wall.
To reduce the incidence of re-obstruction and restenosis, several strategies have been developed. Implantable devices, such as stents, have been used to reduce the rate of angioplasty related re-obstruction and restenosis. The stent is placed inside the blood vessel after the angioplasty has been performed. A catheter typically is used to deliver the stent to the arterial site to be treated.
Another strategy for treating the incidence of re-obstruction and restenosis, as well as other vascular problems, includes the use of therapeutic agents or drugs. Therapeutic agents may be delivered locally or systemically. Stents capable of delivering one or more therapeutic agents have been used to treat the damaged vessel and reduce the incidence of deleterious conditions including thrombosis and restenosis. One drawback to the use of a stent for agent delivery is that stent insertion and implantation may cause undesirable reactions such as inflammation, infection, thrombosis, and proliferation of cell growth that occludes the passageway.
One drawback to systemic delivery of therapeutic agents to a vascular treatment site is that the dosage of the required agent to adequately treat the condition may be too high to achieve a therapeutic dose at the treatment site or may be toxic to the patient.
It is an object of this invention, therefore, to provide a device for effective, controlled delivery of therapeutic agents to a treatment site. It is a further object to provide a system and method for treating heart disease and other vascular conditions, that overcome the deficiencies and limitations described above